From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 21877 invoked by alias); 11 May 2015 20:53:23 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 21868 invoked by uid 89); 11 May 2015 20:53:22 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.2 required=5.0 tests=AWL,BAYES_00,KAM_LAZY_DOMAIN_SECURITY autolearn=no version=3.3.2 X-HELO: rock.gnat.com Received: from rock.gnat.com (HELO rock.gnat.com) (205.232.38.15) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-SHA encrypted) ESMTPS; Mon, 11 May 2015 20:53:12 +0000 Received: from localhost (localhost.localdomain [127.0.0.1]) by filtered-rock.gnat.com (Postfix) with ESMTP id 01B121163E1; Mon, 11 May 2015 16:53:11 -0400 (EDT) Received: from rock.gnat.com ([127.0.0.1]) by localhost (rock.gnat.com [127.0.0.1]) (amavisd-new, port 10024) with LMTP id TQfNJpOLianh; Mon, 11 May 2015 16:53:10 -0400 (EDT) Received: from joel.gnat.com (localhost.localdomain [127.0.0.1]) by rock.gnat.com (Postfix) with ESMTP id C681F1163DA; Mon, 11 May 2015 16:53:10 -0400 (EDT) Received: by joel.gnat.com (Postfix, from userid 1000) id 31DE640DAA; Mon, 11 May 2015 13:53:12 -0700 (PDT) Date: Mon, 11 May 2015 20:53:00 -0000 From: Joel Brobecker To: Pedro Alves Cc: gdb-patches@sourceware.org, Jerome Guitton Subject: Re: [RFA/commit] Memory leak in on reading frame register Message-ID: <20150511205312.GE4767@adacore.com> References: <1431100524-7793-1-git-send-email-brobecker@adacore.com> <55508A83.3060605@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55508A83.3060605@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SW-Source: 2015-05/txt/msg00262.txt.bz2 > > When using a conditional breakpoint where the condition evaluated > > to false a large number of times before the program stopped, > > a user reported that GDB's memory consumption was growing very > > quickly until it ran out of memory. > > > > The problem was tracked down to temporary struct values being created > > each time the program stops and we evaluate those conditions. This > > patch fixes the issue by releasing the temporary values, and adds > > a comment explaining why we do that. > > > > gdb/ChangeLog: > > > > Jerome Guitton : > > * findvar.c (read_frame_register_value): Fix a memory leak. > > > > Tested on x86_64-linux. No regression. > > > > Not sure about this. > > How come this in bpstat_check_breakpoint_conditions didn't > handle this issue already? : > > ... > /* We use value_mark and value_free_to_mark because it could > be a long time before we return to the command level and > call free_all_values. We can't call free_all_values > because we might be in the middle of evaluating a > function call. */ > struct value *mark = value_mark (); > > ... > value_free_to_mark (mark); An excellent question, which I will try to research in the next couple of days! ... > Otherwise, what is releasing other kinds of temporary values? > Are we leaking them? E.g., with: > > int global_val; > void foo () {} > int main () { while (1) foo (); } > > and then: > > (gdb) break foo if global_var == 1 > > an/or: > > (gdb) break foo if (global_var + 1) == 2 > > > Maybe nothing breaks with this patch as its deleting register lval > values, but the case above would involve lval_memory values, > and if we did something for those like in this patch, I fear > that places that want to walk an expression's value chain, > like update_watchpoint / can_use_hardware_watchpoint would break. But I confess I don't quite understand what you mean by the above. Are you saying that the current patch may be OK (because we're creating and deleting a value that we know is independent of all other values), but that it sets a precendent for other forms where it might not be OK? -- Joel